From d7ac6cf6751a0ffa00f9e46022024f79b0daa771 Mon Sep 17 00:00:00 2001 From: Alexander Popov Date: Tue, 28 Feb 2017 19:54:40 +0300 Subject: [PATCH 1/1] tty: n_hdlc: get rid of racy n_hdlc.tbuf commit 82f2341c94d270421f383641b7cd670e474db56b upstream. Currently N_HDLC line discipline uses a self-made singly linked list for data buffers and has n_hdlc.tbuf pointer for buffer retransmitting after an error. The commit be10eb7589337e5defbe214dae038a53dd21add8 ("tty: n_hdlc add buffer flushing") introduced racy access to n_hdlc.tbuf. After tx error concurrent flush_tx_queue() and n_hdlc_send_frames() can put one data buffer to tx_free_buf_list twice. That causes double free in n_hdlc_release(). Let's use standard kernel linked list and get rid of n_hdlc.tbuf: in case of tx error put current data buffer after the head of tx_buf_list. Signed-off-by: Alexander Popov Signed-off-by: Greg Kroah-Hartman Signed-off-by: Ben Hutchings --- drivers/tty/n_hdlc.c | 132 ++++++++++++++++++++++--------------------- 1 file changed, 69 insertions(+), 63 deletions(-) diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c index adb8d01de91e..b2b096beb870 100644 --- a/drivers/tty/n_hdlc.c +++ b/drivers/tty/n_hdlc.c @@ -115,7 +115,7 @@ #define DEFAULT_TX_BUF_COUNT 3 struct n_hdlc_buf { - struct n_hdlc_buf *link; + struct list_head list_item; int count; char buf[1]; }; @@ -123,8 +123,7 @@ struct n_hdlc_buf { #define N_HDLC_BUF_SIZE (sizeof(struct n_hdlc_buf) + maxframe) struct n_hdlc_buf_list { - struct n_hdlc_buf *head; - struct n_hdlc_buf *tail; + struct list_head list; int count; spinlock_t spinlock; }; @@ -137,7 +136,6 @@ struct n_hdlc_buf_list { * @backup_tty - TTY to use if tty gets closed * @tbusy - reentrancy flag for tx wakeup code * @woke_up - FIXME: describe this field - * @tbuf - currently transmitting tx buffer * @tx_buf_list - list of pending transmit frame buffers * @rx_buf_list - list of received frame buffers * @tx_free_buf_list - list unused transmit frame buffers @@ -150,7 +148,6 @@ struct n_hdlc { struct tty_struct *backup_tty; int tbusy; int woke_up; - struct n_hdlc_buf *tbuf; struct n_hdlc_buf_list tx_buf_list; struct n_hdlc_buf_list rx_buf_list; struct n_hdlc_buf_list tx_free_buf_list; @@ -160,6 +157,8 @@ struct n_hdlc { /* * HDLC buffer list manipulation functions */ +static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list, + struct n_hdlc_buf *buf); static void n_hdlc_buf_put(struct n_hdlc_buf_list *list, struct n_hdlc_buf *buf); static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list); @@ -209,16 +208,9 @@ static void flush_tx_queue(struct tty_struct *tty) { struct n_hdlc *n_hdlc = tty2n_hdlc(tty); struct n_hdlc_buf *buf; - unsigned long flags; while ((buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list))) n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, buf); - spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags); - if (n_hdlc->tbuf) { - n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, n_hdlc->tbuf); - n_hdlc->tbuf = NULL; - } - spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags); } static struct tty_ldisc_ops n_hdlc_ldisc = { @@ -284,7 +276,6 @@ static void n_hdlc_release(struct n_hdlc *n_hdlc) } else break; } - kfree(n_hdlc->tbuf); kfree(n_hdlc); } /* end of n_hdlc_release() */ @@ -403,13 +394,7 @@ static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty) n_hdlc->woke_up = 0; spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags); - /* get current transmit buffer or get new transmit */ - /* buffer from list of pending transmit buffers */ - - tbuf = n_hdlc->tbuf; - if (!tbuf) - tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list); - + tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list); while (tbuf) { if (debuglevel >= DEBUG_LEVEL_INFO) printk("%s(%d)sending frame %p, count=%d\n", @@ -421,7 +406,7 @@ static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty) /* rollback was possible and has been done */ if (actual == -ERESTARTSYS) { - n_hdlc->tbuf = tbuf; + n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf); break; } /* if transmit error, throw frame away by */ @@ -436,10 +421,7 @@ static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty) /* free current transmit buffer */ n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf); - - /* this tx buffer is done */ - n_hdlc->tbuf = NULL; - + /* wait up sleeping writers */ wake_up_interruptible(&tty->write_wait); @@ -449,10 +431,12 @@ static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty) if (debuglevel >= DEBUG_LEVEL_INFO) printk("%s(%d)frame %p pending\n", __FILE__,__LINE__,tbuf); - - /* buffer not accepted by driver */ - /* set this buffer as pending buffer */ - n_hdlc->tbuf = tbuf; + + /* + * the buffer was not accepted by driver, + * return it back into tx queue + */ + n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf); break; } } @@ -750,7 +734,8 @@ static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file, int error = 0; int count; unsigned long flags; - + struct n_hdlc_buf *buf = NULL; + if (debuglevel >= DEBUG_LEVEL_INFO) printk("%s(%d)n_hdlc_tty_ioctl() called %d\n", __FILE__,__LINE__,cmd); @@ -764,8 +749,10 @@ static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file, /* report count of read data available */ /* in next available frame (if any) */ spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock,flags); - if (n_hdlc->rx_buf_list.head) - count = n_hdlc->rx_buf_list.head->count; + buf = list_first_entry_or_null(&n_hdlc->rx_buf_list.list, + struct n_hdlc_buf, list_item); + if (buf) + count = buf->count; else count = 0; spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock,flags); @@ -777,8 +764,10 @@ static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file, count = tty_chars_in_buffer(tty); /* add size of next output frame in queue */ spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock,flags); - if (n_hdlc->tx_buf_list.head) - count += n_hdlc->tx_buf_list.head->count; + buf = list_first_entry_or_null(&n_hdlc->tx_buf_list.list, + struct n_hdlc_buf, list_item); + if (buf) + count += buf->count; spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock,flags); error = put_user(count, (int __user *)arg); break; @@ -826,14 +815,14 @@ static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp, poll_wait(filp, &tty->write_wait, wait); /* set bits for operations that won't block */ - if (n_hdlc->rx_buf_list.head) + if (!list_empty(&n_hdlc->rx_buf_list.list)) mask |= POLLIN | POLLRDNORM; /* readable */ if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) mask |= POLLHUP; if (tty_hung_up_p(filp)) mask |= POLLHUP; if (!tty_is_writelocked(tty) && - n_hdlc->tx_free_buf_list.head) + !list_empty(&n_hdlc->tx_free_buf_list.list)) mask |= POLLOUT | POLLWRNORM; /* writable */ } return mask; @@ -859,7 +848,12 @@ static struct n_hdlc *n_hdlc_alloc(void) spin_lock_init(&n_hdlc->tx_free_buf_list.spinlock); spin_lock_init(&n_hdlc->rx_buf_list.spinlock); spin_lock_init(&n_hdlc->tx_buf_list.spinlock); - + + INIT_LIST_HEAD(&n_hdlc->rx_free_buf_list.list); + INIT_LIST_HEAD(&n_hdlc->tx_free_buf_list.list); + INIT_LIST_HEAD(&n_hdlc->rx_buf_list.list); + INIT_LIST_HEAD(&n_hdlc->tx_buf_list.list); + /* allocate free rx buffer list */ for(i=0;ispinlock, flags); + + list_add(&buf->list_item, &buf_list->list); + buf_list->count++; + + spin_unlock_irqrestore(&buf_list->spinlock, flags); +} + /** * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list - * @list - pointer to buffer list + * @buf_list - pointer to buffer list * @buf - pointer to buffer */ -static void n_hdlc_buf_put(struct n_hdlc_buf_list *list, +static void n_hdlc_buf_put(struct n_hdlc_buf_list *buf_list, struct n_hdlc_buf *buf) { unsigned long flags; - spin_lock_irqsave(&list->spinlock,flags); - - buf->link=NULL; - if (list->tail) - list->tail->link = buf; - else - list->head = buf; - list->tail = buf; - (list->count)++; - - spin_unlock_irqrestore(&list->spinlock,flags); - + + spin_lock_irqsave(&buf_list->spinlock, flags); + + list_add_tail(&buf->list_item, &buf_list->list); + buf_list->count++; + + spin_unlock_irqrestore(&buf_list->spinlock, flags); } /* end of n_hdlc_buf_put() */ /** * n_hdlc_buf_get - remove and return an HDLC buffer from list - * @list - pointer to HDLC buffer list + * @buf_list - pointer to HDLC buffer list * * Remove and return an HDLC buffer from the head of the specified HDLC buffer * list. * Returns a pointer to HDLC buffer if available, otherwise %NULL. */ -static struct n_hdlc_buf* n_hdlc_buf_get(struct n_hdlc_buf_list *list) +static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *buf_list) { unsigned long flags; struct n_hdlc_buf *buf; - spin_lock_irqsave(&list->spinlock,flags); - - buf = list->head; + + spin_lock_irqsave(&buf_list->spinlock, flags); + + buf = list_first_entry_or_null(&buf_list->list, + struct n_hdlc_buf, list_item); if (buf) { - list->head = buf->link; - (list->count)--; + list_del(&buf->list_item); + buf_list->count--; } - if (!list->head) - list->tail = NULL; - - spin_unlock_irqrestore(&list->spinlock,flags); + + spin_unlock_irqrestore(&buf_list->spinlock, flags); return buf; - } /* end of n_hdlc_buf_get() */ static char hdlc_banner[] __initdata = -- 2.39.2